1. Field of the Invention
The present invention relates to a control method of a light source unit comprising a filament lamp, a light source control unit and a light source unit, and more particularly, to a control method of a light source unit comprising a filament lamp with a characteristic of having a light quantity changing almost in proportion to a control voltage, and a light source control unit, and a light source unit.
2. Description of the Related Art
As a light source unit where the illuminance of the filament lamp is changed, it is a commonly used method to employ a voltage stabilizer in the light source unit comprising a filament lamp. FIG. 2 shows the simplest method in which a control voltage 1Vc changes an applied voltage 5V of the lamp so that a luminous flux 8 Lm of the filament lamp is changed.
Continuing with FIG. 2, the voltage 5V applied to the lamp is proportionate to the voltage of the control voltage 1 Vc, and the voltage applied to the lamp at the maximum control voltage is set in such a manner that it becomes a rated voltage of the lamp. Although such a light source unit is priced moderately, it has a drawback in that an illuminance Lx of the lamp for the control voltage 1Vc is nonlinear with the light quantity thereof changed exponentially as shown in the drawing FIG. 3, and a fine adjustment of setting it to a predetermined light quantity is difficult to perform.
On the other hand, in order to change the illuminance of this lamp in proportion to the control voltage, there are two methods conceivable. One method is to turn an inverse transformation corresponding to the nonlinearity of the light quantity for the control voltage into the control voltage. The other method is to feed back the light quantity and make a monitor light proportionate to the control voltage. These methods, however, make the units complicated, thereby making it difficult to manufacture the control units at a moderate price.